The red squirrel is still widespread throughout the island of Ireland, although its distribution can be quite patchy. The grey squirrel has spread through the eastern half of the country, and in certain midland areas where the grey has been longest established, red squirrels have disappeared. Greys continue to spread to the northwest and southwest, but moves to the west of Ireland have been halted by unsuitable terrain, with the River Shannon delineating the western extreme of their distribution. Red squirrels continue to disappear from forests into which the grey squirrels have invaded, and there has been a 20% decline in their range in the one hundred years since the grey squirrel arrived, with half of that decline occurring in the last ten years.
